Summarize the means by which the polygraph works as a lie detector. What two major problems call its accuracy into question?

What will be an ideal response?

A polygraph is an instrument that records physiological arousal from multiple channels.
The assumption underlying its use is that when a suspect lies, he or she becomes
anxious in ways that can be measured—specifically, through changes in breathing,
blood pressure, and perspiration. First, the suspect's baseline level of arousal is
established. Then, the examiner asks a series of yes-no questions and compares the
suspect's reactions to emotionally arousing crime-relevant questions with his or her
reactions to control questions that are arousing but not relevant to the crime. In theory,
suspects whose denials about the crime are truthful should be more aroused by the
control questions, whereas suspects whose denials are false should be more aroused by
the crime-relevant questions. One problem with the use of the polygraph as a lie
detector is that truthful people often fail the test. A second problem is that the test can
be faked. To avoid being aroused by crime-relevant questions, some guilty individuals
are able to use countermeasures such as distraction or an artificial inflation of their
arousal responses to control questions (by, for example, clenching their toes so that the
arousal observed in their responses to crime-relevant questions does not seem high in
comparison).